Radiation detectors, such as Group II-VI detectors of IR radiation, generally are characterized as having an energy bandgap that is suitable for absorbing radiation within a single spectral region. As such, a capability to detect, with a single detector, radiation within more than one spectral region is a desirable goal. However, presently available technology for realizing this function is less than optimum. For example, two separate focal planes can be provided in conjunction with an optical device for spectrally splitting an incident radiation beam, thereby directing a portion of the beam to each of the focal planes. However, this approach requires relatively complicated optical devices and optical alignment and further requires the expense associated with two focal planes of radiation detectors.
Another approach involves a wedge filter for spectrally dispersing an incident radiation beam. However, the wedge filter is relatively difficult to fabricate and align and does not provide spatial concurrency of detected radiation. Furthermore, the wedge filter approach is not amenable to the fabrication of a staring-type radiation detecting array.
Another approach involves a binary optic spectral spreading technique. However, this technique requires a separate connection, typically an indium bump, for each detected spectral region (or color). This approach also requires a separate readout cell for each detected color. Also, the alignment and patterning of the required binary optic pattern is difficult to accomplish and may result in a reduced yield.
It is thus an object of the invention to provide method and apparatus for sensing more than one spectral band of radiation with a single radiation detector.
It is another object of the invention to provide method and apparatus for sensing at least two spectral bands with a single two-terminal radiation detector.
It is one further object of the invention to provide a two-terminal radiation detecting device and an array of same responsive to at least two discrete IR spectral bands.